Device for reducing noise in multicylinder piston machines



Dec. 13, 1960 G. WIGGERMANN 2,963,983

CYLINDER PISTON MACHINES DEVICE FOR REDUCING NOISE IN MULTI- Filed Oct. 1, 1957 8 Sheets-Sheet 1 FIG.\

rqFim Dec. 13, 1960 G. WIGGERMANN 2,963,983

DEVICE FOR REDUCING NOISE IN MULTI-CYLINDER PISTON MACHINES Filed Oct. 1, 1957 8 Sheets-Sheet 2' my. a

Dec. 13, 1960 G. WIGGERMANN 2,963,983

DEVICE FOR REDUCING NOISE IN MULTI-CYLINDER PIS TON MACHINES Filed Oct. 1, 1957 s Sheets-Sheet 3 Dec. 13, 1960 G. WIGGERMANN 2,963,933

DEVICE FOR REDUCING NOISE IN MULTI-CYLINDER PISTON MACHINES Filed Oct. 1, 1957 8 Sheets-Sheet 4 u 22b 214 {199 20:,215 13 b PRR Dec- 13, 1960 G. WIGGERMANN 63,983

DEVICE FOR REDUCING NOISE IN MULTI-CYLINDER PISTON MACHINES Filed Oct. 1, 1957 8 Sheets-Sheet 5 Fig. 5.

Dec. 13, 1960 e. WIGGERMANN 2,963,933

DEVICE FOR REDUCING NOISE. IN MULTI-CYLINDER PISTON MACHINES Filed Oct. 1, 1957 a Sheets-Sheet 7 Jfa DPR

NI V Dec. 13, 1960 WIGGERMANN 2,963,983

DEVICE FOR REDUCING NOISE IN MULTI-CYLINDER PISTON MACHINES Filed Oct. 1, 1957 8 Sheets-Sheet 8 United States Patent DEVICE FOR REDUCING NOISE iN MULTI- CYLINDER PISTON MACHINES Georg Wiggermann, Spitzgartenweg l0 Kressbronn, Germany, assignor of one-half to WalterReiners, M. Gladbach, Germany filed 0a. 1, 1951, Ser. No. 687,490

Claims priority, application Germany Oct. 1, 1956 31 Claims. (CL 103-162) My invention relates to devices for reducing noise in hydraulic piston machines operable as motors or pumps, and particularly in machines of the type having a rotating multi-cylinder assembly with reciprocable pistons that rotate together with the cylinder assembly.

The operation of piston machines with a liquid pressure medium requires a periodic on and off connection of the variable-volume cylinder chambers with the hydraulic flow circuit, which causes corresponding pressure variations in these chambers, occurring in most cases at relatively high frequency. The forces acting upon the pistons vary proportionally to the pressure and impose corresponding alternating mechanical stresses upon all components of the piston-machine mechanism including its housing.

such machines for controlling the periodic supply and discharge of hydraulic operating medium relative to the variable-volume chambers of the machine cylinders.

. Pump, direction of 2,963,983 Patented Dec. 13, 1960 in the cylinder chamber effects a relatively slow expansion or compression of the enclosed hydraulic medium; The result, under most favorable conditions, is that at the moment when the cylinder chamber starts communi= eating with the control opening or slot of the rotary ice . valve, there already exists equality of pressure between cylinder chamber and valve slot so that the noise-producing abrupt change in pressure is eliminated to a great extent.

However, such optimum conditions are the exception; and a more thorough investigation shows that the angle of rotation of the rotary control valve during which the individual cylinder chambers, under expansion or compression, are to remain closed, should not be constant but, for best results, must vary in dependence upon structural constants as well as upon several variable operating parameters, such as the hydraulic delivery pressure (p -p and the stroke ratio (H/H Further dependencies of the magnitude and the sign or of the compression angle or expansion angle of the rotary valve control means exist, particularly with piston machines of regulatable piston stroke, in accordance with the particular correlation between the direction of rotation and the direction of hydraulic delivery and the selected operation as a pump or a motor. The latter dependencies comprise eight different operation possibilities of variable operation. These eight diflerent types of machine operation are tabulated in the following table. The symbols used in the table are defined below under the heading Definitions. The sign of the compression angle a and the expansion angle a, denote only the direction of variation of the respective angles but not their absolute magnitude. A noise reducing device, in order to operate satisfactorily, must contain structural means which perform the automatic basic regulation in accordance with the table, and it must also comprise additional devices which automatically determine the absolute magnitude of the angle a and a requiredfor the necessary equalization of pressures.

TABLE rotation CL, flow direction of medium x Motor, direction of rotation ACL, flow direction of medium y Pump, direction of rotation CL, flow direction of medium y Motor, direction of rotation ACL, flow direction of medium 2:

. Pump, direction of rotation ACL, flow direction of medium y Motor, direction of rotation CL, flow direction of medium x Pump, direction of rotation ACL, flow direction of medium x b. Motor, direction of rotation CL, flow direction of medium y These devices prolong the switching or pressure-commutating operation of the slide valve by providing the valve with throttle cross sections. However, such throttle cross sections always cause power losses, and their efiect varies with the speed of rotation. For that reason, further means have been proposed which operate to keep the cylinder spaces individually closed over a certain angle In a device for noise reduction, the above-mentioned dependencies must be taken into account insofar as the tabulated controlling magnitudes may occur in the desired particular operation of the machine. Accordingly, proposals have become known which achieve the change in compression or expansion angle of the rotary control valve by correspondingly turning the valve member that carries the control openings or slots. Such devices, however, have the disadvantage of requiring a very complis,ces,sss

3 cated construction and exhibiting very difficult pressure sealing problems.

It is further impossible with the known proposals to individually vary the compression and expansion angles by amounts ditfering from each other.- This is so because the members that carry the control openings or '4 p =pressure in the suction slot=slot of lower pressure p ==pressure in the pressure slot=slot of higher pressure p =control pressure for the piston in the range of .the one valve slots permit only a single angular adjustment to be f effective simultaneously for all valve openings. This makes it impossible, for instance, to take into account the fact that the compression chambers in the cylinders are difierent in the inner and outer dead-center position of the piston respectively. a

It is therefore one of the objects of my invention to provide noise reducing devices for rotary cylinder machines of the above-mentioned type, which atford satisfying in a favorable manner all requirements as regards the variable and constant magnitudes upon which the abovementioned pressure adaptation is predicated, thus permitting a better and more reliable noise reduction than obtainable with the devices heretofore known.

To this end, and in accordance with one of the fea tures of my invention, I provide the control slots (main slots) of the rotary control valve, serving for periodically connecting the individual variable-volume cylinder chambers with the suction and pressure ducts of the control valve, with a number of component openings (hereinafter called auxiliary slots) located near the respective ends of the valve slots; and I further provide the device with hydraulic valve-type switching devices which automatically vary the opening angle of the rotary control valve by connecting and disconnecting the just-mentioned auxiliary slots relative to the main control slots. 1

The foregoing and more specific objects, advantages and features of my invention, the essential features being set forth with particularity in the claims annexed hereto, will be apparent from, and will be mentioned in, the following description of the embodiments illustrated on the drawings in which:

Fig. 1 is a schematic sectional view of a multi-cylinder hydraulic machine exemplifying the general kind of machinery with which the invention is applicable; and

Fig. 2 is a top view onto the valve control face of the lower rotary valve member forming part of the machine shown in Fig. 1.

Fig'. 3 is a schematic view onto the control slots in the control face of a rotary slide valve, in conjunction with other components of a noise reducing device according to the invention.

Figs. 4, 5 and 6 illustrate schematically three dilferent modifications of such noise reducing devices.

Fig. 7 illustrates schematically a complete control system including the valve control slots and a number of hydraulic switching and pressure regulating components.

Fig. 8 is a modification of a complete system somewhat similar to that of Fig. 7.

Fig. 9 illustrates schematically a multiple valve-type switching device applicable in devices according to the invention.

Fig. 10 illustrates schematically a pressure regulator also for devices according to the invention.

Fig. 11 illustrates schematically another multiple hy- Definitions The following symbols and abbreviations arev used throughout this specification:

p=delivery pressure=pressure diflerence p;p

neutral zone that comprises the inner dead-center position of the piston p,,=control pressure for the piston in the range of the other neutral zone comprising the outer dead-center position of the piston p =pressure of an auxiliary hydraulic path, for instance produced by a leakage oil pump p,=a pressure equal or proportional to the difference pressure p p,=pressure in the cylinder (variable-volume chamber) V,=cylinder volume at V =zero (zero stroke adjustment) V =cylinder volume at the inner dead-center point of the piston I V =cylinder volume at the outer dead-center position of the piston V=stroke volume of a piston at a rotation angle a of the rotary valve slider V =wdisplacement volume of a piston at full stroke, corresponding to =180 +V =machine operates clockwise (CL) as a pump, or

anticlockwise (ACL) as a motor; under these conditions p obtains in control slot 111, and pressure p, obtains in control slot 11:

V machine operates clockwise (CL) as motor or anti-clockwise (ACL) as pump; then p obtains in control slot 1a, p, in control slot 1b e=rotation angle of the rotary slide valve or of the stroke-producing shaft, measured from the dead-center position of the piston a =compression angle=rotation angle of the strokeproducing shaft or of the rotary slide valve, during which angle the pressure p, increases when the cylinder chamber is closed .=expansion angle=rotation angle of the stroke-producing shaft or of the rotary slide valve, during which angle the pressure p, declines when the cylinder chamber is closed a =rotation angle which results in a displacement volume V on the V -side of the valve control face (measured from the neutral axis) ,=rotation angle which results in a volume variation V on the V -side of the valve control face (measured from the neutral axis) =positive compression angle; i.e. mg is adjacent to the neutral axis with clockwise (CL) rotation a =negative compression angle; i.e. el is adjacent to the neutral axis with anti-clockwise (ACL) rotation +a,=positive expansion angle; i.e. a, is adjacent to the neutral axis with clockwise (CL) rotation --,=negative expansion angle; i.e. a, is adjacent to the neutral axis with anti-clockwise (ACL) rotation +a =positive compression angle in the range of the inner dead-center point -a =negative compression angle in the range of the inner dead-center point =positive compression angle in the range of the outer dead-center point =negative compression angle in the range of the outer dead-center point =positive expansion angle in the range of the inner dead-center point u, =negative expansion angle in the range of the inner deadeenter point +e =positive expansion angle in the range of the outer dead-center point a =negative expansion angle in the range of the outer deadcenter point C =elasticity constant of the liquid working medium C,=elasticity constant of the cylinder volume V, including the stroke-producing mechanism component (,=spring constant of the elastic means, such as springs or the like, with which the reciprocable pistons are loaded CL=clockwise sense of rotation ACL=anti-clockwise sense of rotation NA=neutral axis=imaginary line on the control face of the rotary slide valve which bisects the centering angle of the cylinder port at the moment when the apper taining piston is in a dead-center position Generally, machines of the type here involved have pistons reciprocating in respective cylinder bores which are distributed about the drive shaft and extend in parallel, inclined or radial relation thereto. The individual cylinders are sequentially connected, in timed relation to the periodic piston reciprocations, with stationary valve slots for supplying and discharging the hydraulic working medium. For this purpose, the member or drum in which the cylinder bores are located is rotatable in face-to-face engagement with a fixed valve surface and is provided with ports which periodically establish a communication between the respective cylinder bores and the valve slots of the fixed valve surface (control face of the valve). The rotating member thus forms together with the fixed valve surface a valve device of the rotary slide-valve type; and the invention proper concerns itself with noise reducing devices that include, or coact with, such rotary slide-valve devices.

The two mutually engaging surfaces of the rotary slide-valve device may have any suitable cooperating shape. For example, in Figs. 1 and 2 these surfaces are illustrated as being planar, at K. As mentioned, each cylinder port opens into the valve surface of the cylinder member and travels periodically over the slots in the fixed control face of the valve during rotation of the cylinder member so that a temporary communication is established between the slots and the ports. This will be more fully understood with reference to the machine exemplified by Figs. 1 and 2.

FIGS. 1 AND 2 The illustrated hydraulic multi-cylinder machine has a stationary housing A in which a slanting control body B is mounted. The housing is axially traversed by a shaft D on which a drum-shaped cylinder structure E is mounted. The cylinder drum E has a number of cylinders F formed by bores uniformly distributed about the shaft D and extending parallel to the shaft axis. Pistons G are reciprocable in the respective cylinder bores. Each cylinder bore has a port 5 which, in the proper rotational position of the cylinder bore, communicates with one of two control slots 1a or 1b in a planar valve surface K of the housing assembly. The slots 1a and 1b are connected with oil inlet and outlet lines respectively.

Assuming that the machine is operating as a pump, the shaft D is driven to rotate the cylinder structure E while the oil lines are under pressure. During rotation of the cylinder structure E, the pistons G, in gliding engagement with the control surface of member B, are periodically moved into and out of the cylinder bores F so as to form respective variable-volume chambers together with the cylinder structure. The piston G shown in lowermost position at the left side of the illustration moves upwardly and inducts oil through the inlet slot and the port 5 until it almost reaches the uppermost position of the piston G shown at the outermost right of the cylindcr drum. Thereafter the .port 5 is connected with the outlet slot 1b, and the pIston is forced back into the cylinder to deliver oil into the slot lb, proper check valves being provided in the inlet and outlet lines as usual for such purposes.

It should be noted, however, that for the purpose of illustration, the valve memberA in Fig. 1 is shown 90 7 turned from its correct position. That is, the lowermost axis NA indicated by a vertical dot-and-dash center lin in Fig. 2; and the two valve slots 1a and 1b lie symmetrical to that center line, also as shown in Fig. 2.

Fig. 2 also shows one of the two hydraulic lines L that communicate with the valve slots 1a and 1b respectively and hence also with the individual ports 5 and cylinder chambers F then registering with the respective slots.

In hydraulic machines having a constant length of piston stroke the control body B is fixed and may form part of the machine housing or be rigidly joined therewith. In machines having an adjustable piston stroke for control of delivery, the desired adjustability can be obtained, for example, by making the control body B adjustable as regards its angle of inclination. In the embodiment illustrated by way of example, the control body B is mounted on a calotte-shaped body P which can be angularly displaced in housing A by means of an arm Q. When arm Q is in central position, i.e. coaxi-ally aligned with the axis of shaft D, the control body lies horizontal, and the piston stroke is zero so that the hydraulic delivery during rotation of the cylinder drum is also zero. Arm Q can be shifted from the zero position to the right or left to set any desired piston stroke length within the available range of positive and negative directions of delivery.

Now, according to the invention, each of the valve slots 1a, 1b has both of its ends in the direction of rotation subdivided into a number of auxiliary slots such as those denoted in Figs. 2 and 3 by 20, 3a, 4a, and 2d, 3d, 4d for slot 1a, and by 2b, 3b, 4b, and 2c, 30, 4c for slot 1b (Fig. 3). These partitioned-off slots, hereinafter called auxiliary slots are in communication with respective ducts or lines such as those shown at 6a, 7a, 8a and 6d, 7d, 8d in- Fig. 2, through which each auxiliary slot can communicate with the adjacent main slot 1a or 1b under control by a hydraulic, valve-type slot control switch described below with reference to Fig. 3 and the other embodiments. It will be apparent that by virtue of such a control device, the angular or arcuate length of the slots 1a and 1b in each quadrant of the valve control face or circle of machine rotation can be lengthened and shortened.

Before explaining this more in detail, it may be mentioned that relative to the invention still more fully to be described, the particular machine design here used by way of example is not essential except for the basic feature, mainly the slots and parts, of the rotary slide valve and these may be incorporated into hydraulic machines having cylinders mutually oriented in directions other than as specifically illustrated and described herein. The arrangement and structural design of the hydraulic circuitry is likewise not essential, the term line being used herein to denote a hydraulic circuit connection regardless of whether it is formed by bores, hollows or ducts in the valve members or machine components themselves or whether pipes or other tubing are used.

FIG. 3

Of the above-described hydraulic machine, Fig. 3 shows schematically only the main slots 1a and 1b of the valve control face and the auxiliary slots 2a, 3a, 4a; 2b, 3b, 4b; 20, 3c, 4;; and 2d, 3d, 4d. It is assumed, as an example, that the cylinder body (E in Fig. 1) cooperating with the valve slots has seven cylinders. The seven cylinder ports 5 are indicated by dot-and-dash lines. The vertical center line NA-NA indicates the neutral axis.

The auxiliary slots 2a, 3a, and 4a are connected through respective hydraulic lines, 6a, 7a, 8a with one of four switching devices of slide-valve type. The auxiliary slots 2b, 3b, 4b are connected with another one of the switching devices through hydraulic lines 6b, 7b, 8b. The auxiliary slots 20, 3c, 40 are connected through lines 6c, 7c, 8c with the third device; and the slots 2d, 3d, 4d are connected through lines 6d, 7d, 8d with the fourth switching device. The four switching devices comprise respective cylinder sleeves 9a, 9b, 9c and 9d in which respective piston sliders 10a, 10b, 10c and 10d are displaceably guided and sealed foroil pressure. Aside from the above-mentioned hydraulic lines, two further lines 11a, 11b extend from control slot la'to cylinder sleeves 9a and 9b respectively; and corresponding lines 11c, 11d connect control slot 1b with the respective sleeves 9c and 9d.

Each of the piston sliders 10a, 10b, 10c and 10d has a constricted portion 12a, 12b, 12c or 12d whose axial length is such as to embrace all port openings of the respective line groups such as 6a, 7a, 80, 11a. During axial movement ofthe piston sliders, they are unilaterally loaded by respective pressure springs 13a, 13b,'13c and 13d. Each spring abuts against a set screw 14 secured in a threaded cap 15.

A further hydraulic line 16a connects the control slot 1a with the pressure spaces 17a and 17c of the two sleeves 9a and 9c, and with spring spaces of the two other sleeves 9b and 9d. Similarly, another line 16b connects .control slot 1b with the pressure spaces 17b, 17d of sleeves 9b, 9d and with the spring spaces of sleeves 9a and 9c.

All hydraulic lines are illustrated in single-line fashion; hydraulic junctions between the lines are indicated by dots, the crossing of lines as such being understood not to involve a hydraulic connection.

The operation is as follows.

The illustrated position of the piston sliders corresponds to a pressure difference p,p -zero. The pressures p, and p in respective control slots 1a, 1b may have any value up to the rated permissible maximum. According to definition of p, and p (see above), p, is always equal to or larger tha P1; and the control slot of the control face possessing this pressure p, is hereinafter designated.

as the pressure slot, whereas the control slot subjected to the pressure p is called the suction slot.

In the illustrated position of pressure balance (p==p the constrictions 12 (a to d) of the piston sliders connect all respective lines 6 (a-d), 7 (a-d), 8 (a-d), 11 (ad) and hence all auxiliary slots 2,3, 4 with the correlated control slots 1a or 1b. During CL-rotation of the cylinder ports 5, these ports travel once over both control slots during each full rotation and are thus alternately subjected to the pressures p and 11,. The pressures p and p of course, are also identical with the operating pressure in the hydraulic connecting lines (L in Fig. 2) of the multi-cylinder machine itself, since these connecting lines (L) directly communicate with the respective control slots 1a, 1b. I

For explanation, assume that the uppermost cylinder port which in Fig. 3 is just travelling across the NA axis appertains to a cylinder whose displacer member (piston G in Fig. l) is in V -position, i.e. in outer dead center, so that after further rotation of a=l80 this particular cylinder will reach the V -position, i.e. the inner dead-center point. With CL-rotation of the cylinder body (E in Fig. 1) and its cylinder ports 5, the fore- I going assumption corresponds to a positive value of +V and the hydraulic machine operates either as a pump of constant piston stroke in CL-rotation, or as a motor in ACL-rotation. Under both conditions, the pressure p, obtains in the control slot 1b so that this slot represents the pressure slot, while slot 1a is the suction slot.

The uppermost cylinder port 5 (Fig. 3) when passing across the NA axis has just left the last auxiliary slot 2a of the suction slot 1a. Hence the cylinder volume V, is subjected to the pressure p The first auxiliary slot 2b of pressure slot 1b already possesses the full pressure At pressure balance 01 1 no pressure change takes place in the cylinder and therefore no noise is produced.

Disregarding for a moment the efiect of the auxiliary means slots, it would appear that, as soon as the pump takes up hydraulic power so that p, becomes larger than p an almost sudden increase from p up to p, would occur in the stroke space of the cylinder which would tend to produce noise dependent, among other things, upon the magnitude of the pressure difierence. After rotation of 1:180", a reverse equalization of the cylinder pressure from p, toward p would occur just as suddenly as the cylinder port 5 eommutates from auxiliary pressure slot 2c to auxiliary suction slot 2d. Each such sudden change in cylinder pressure varies the mechanical stresses imposed upon the mechanism and its housing thus excitingsound-produeing oscillations. Y

However, in the device according to Fig. 3 such noisy performance is subdued or eliminated by virtue of the following effects. The pressure dilference pgp acting through hydraulic lines 16a, 16b (pressure 12 being effective in pressure slot 1b), causes a displacement of the piston sliders 10b, 10d toward respective springs 13b and 13d until the increasing spring force and the displacing force caused by p; are just balanced by the displacing force caused by p,. During this equalizing performance, for instance under increasing differential pressure p,p the piston sliders 10b and 10d sequentially disconnect the auxiliary slots 2b, 3b, 4b and 2d, 3d, 4d from the lines 11b, 11a and thus from main slots 1b and 1a respectively. Therefore each cylinder port 5, after passing across the neutral axis NA, encounters an increasing number of closed auxiliary slots of the group 2b, 3b, 4b. During the same angle of rotation, the reciprocating machine piston already reduces the cylinder volume V by an amount which increases with the angle of rotation, so that a pressure increase occurs in the cylinder chamber in accordance with the elasticity constants C C Analogously, the auxiliary slots 2d, 3d, 4d at main slot 1a, during the progressive shortening of the slot group commencing at 4d, cause an increase in cylinder volume V due to the piston movement commencing at this moment. As a result, the cylinder chamber, now remaining closed, is subjected to a reduction in pressure in conjunction with the constants C 0,. In accordance with the law of motion of the machine pistons in dependence upon the angle of rotation is, that is the dependence of the displacement volume V upon the angle a, there is for each pressure drop p=p,p a definite angle c or a, at which the pressure balance will obtain in each cylinder port 5 at the pressure p, or p In accordance therewith, the springs 13 (a to d), if desired in conjunction with a suitable adjustment of the axial spacing between the port openings at which the hydraulic lines (for instance 6a, 7a, 8a, 11a) communicate with the interior of the switch-valve sleeve (9a), are so adjusted by means of the set screws 14 that the displacement of the piston sliders caused by the ditference pressure p -p always automatically regulates the compression or expansion by correspondingly adding and disconnecting the auxiliary slots as required for the desired pressure equalization. This automatic regulation occurs with an accuracy which increases with the number of the auxiliary slots provided.

During the operating condition just described, the pressures 1);, p, also act upon the piston sliders 10a, 100. However, the pressure p, is active in the spring spaces 13a, 13c and the pressure p in the pressure spaces 17a, so that the piston sliders 10a, 10c retain the illustrated positions. Consequently, the slots 2a, 3a, 4a remain fully in hydraulic connection with the control slot la; and the slots 20, 3e, 40 remain fully connected with con- ,trol slot 1b. As a result, the suction slot In, for instance, can fill the cylinder chambers (F in Fig. l) through the ports 5 until the respective ports travel over the neutral axis NA, that is until the pistons (G in Fig. 1) reach the etfective outer dead-center point. Analogously, the variable-volume cylinder chambers are in hydraulic connection with the pressure'slot at the end of the pressure stroke and until the pistons reach the effective inner dead-center point.

In this manner, the noise reducing device satisfies the.

already described. Control slot 1a being new the suction sleeves 9a to 9d of the slot switching devices likewise takes place gradually. Therefore the adding and disconnecting of the individual auxiliary slots takes place with a variable throttling effect. This smoothens in favorable sense the incremental regulation of a and a, stemming from the limited number of the auxiliary slots. With the exception of the throttling component, the described pressure adaptation takes place without losses.

This is so because the work done by the drive during the compression occurring when the variable-volume cylinder space is temporarily closed, is regained by the expansion occurring at the beginning of the suction stroke.

During operation in practice certain operating conditions may occur which cause a reversal in power flow. For example, when in a hydraulic drive comprising a pump and a motor, the hydraulic motor occasionally is subjected to over-hauling load and runs ahead of the pump, the motor temporarily acts reversely as a pump and now drives the pump proper in the original direction of rotation as a motor. Under such conditions, the valve slot normally operating as a suction slot in the control face of the pump, now receives the higher pressure and, in accordance with the definitions of the present specification, must now be considered as the pressure slot, whereas the previous pressure slot becomes the suction slot. The CL-sensc of rotation presumed in the foregoing considerations remains unchanged during such power reversal. When now p, changes over from control slot 1b to control slot 1a, then the piston sliders b and 10d (Fig. 3) remain in the illustrated starting positions, whereas the piston sliders 10a and 100 now connect and disconnect the two groups of auxiliary slots 2a, 3a, 4a and 20, 3c, 4c in dependence upon the pressure difference P3-p1, so that again the angles a and a, are continuously and automatically regulated as required for pressure adaptation. During this operation the cylinder ports 5 are disconnected, or may be disconnected from the control slot 1b, now acting as suction slot, already before the ports 5 reach the inner dead-center point. Analogously, theports 5 may now be disconnected from slot in, now acting as the pressure slot, before the outer dead-center point is reached. At the same time, the auxiliary slots at the other slot end of slots 1b and 1a remain in full communication with the appertaining main slot.

Consequently during such operating conditions the requirements above explained are again satisfied. That is, when operating the machine as a motor, the compression angle a and the expansion angle m always have their full magnitude located ahead of the neutral axis; and the regulation again takes place automatically and without appreciable losses because the compression work done prior to passing through the neutral axis is regained by the expansion work done subsequent to passage through neutral.

If the machine above considered is being operated, with constant stroke and constant sign of V as a pump in ACL-rotation, then all regulating conditions remain as last described except that the delivering direction is reversed, and the entire extent of the angles a; and u, again lies ahead of the neutral axis.

With this AOL-direction of rotation, too, there may occur the case that the power flow reverses itself so that the pump must run as a motor. Under these conditions, the pressures p and p, change their respective slots as slot and slot 1b the pressure slot. As a result, and as will be recognized from the diagram of Fig. 3, the piston sliders 100, 10c again shift into the illustrated starting positions, and the piston sliders 10b, 10d take care of regulating the two respective groups of auxiliary slots 2b, 3b, 4b and 2d, 3d, 4d. This causes'the desired expansion in the individual cylinder chambers to occur in the range of slots 2b, 3b, 4b; and analogously results in the desired compression at slots 2d, 3d, I v

In summary, a hydraulic machine equipped with a noise reducing device according .to Figs. 1, 2 and 3 can be operated satisfactorily in both directions of rotation as a motor as well as a pump. The angles a and or, regulate themselves automatically in the desired sense as to magnitude and sign.

Referring to the above-mentioned table, the types of machine operation described in the foregoing with reference to Fig. 3 correspond to those denoted in the table by Ia, Ib, 111a, IIIb. In all these cases the magnitude V has a positive sign.

When the drive of the displacement members, i.e. the machine pistons, is phase displaced relative to the slide valve control, then this change corresponds to an exchange of the inner and outer dead-center positions and hence to an exchange of V and V as regards their above-assumed respective locations relative to the rotation at the valve control face; and the direction of delivery is reversed under all operating conditions so far considered in the foregoing. The piston machine can then-be run satisfactorily under all operating conditions with a negative sign of V listed in the table as Ila, IIb and -IVa, IVb. These operations merely require connecting the hydraulic line 16a with the control slot 1b, and line 16b with the slot la. This can be done by means of other hydraulic lines or by additional switching valves such as those described further below.

The noise reducing performance of the device described above comes about by virtue of the fact that the increase and decrease of pressure in the individual cylinder chambers is caused to take place over a definitely given angle of rotation of the machine independently of the speed of rotation, the period of time for passing through this angle and hence available for pressure equalization being considerably longer than with slide valve controls not equipped with this device. Furthermore, in the described device the angle of rotation regulates itself automatically in a favorable manner so that with an increasing difference pressure p=p p there is also available an increasing angle of rotation for effecting the pressure equalization. The improved noise reduction is therefore secured under all operating conditions.

In Fig. 3 the elastic means are shown as simple pressure springs 13 (a to d). In order to adapt the regulating operation of the piston sliders to the particular requirements of the given machine performance, difierent possibilities in the design of the progressive angle of pitch of the turns of these springs or in the number of springs per set will occur to one skilled in the art upon reading this disclosure, for securing other desired spring-force characteristics of the springs 13a, 13b, 13c, 13d.

FIG. 4

In the embodiment illustrated in Fig. 4, the control slots 1a, 1b and the appertaining groups of auxiliary slots are exactly the same, with respect to design and position relative to the neutral axis, as described above with reference to Fig. 3. In contrast to Fig. 3, however, the four actuator members or pistonsliders 10a, 10b, 10c, 10d 7 1 l The control slot In (Fig.4) is connected by oil lines In, 11d with the sleeve spaces in which the constrictions 1a and 21d of the piston sliders are located. Control lot lb is similarly connected through lines 11b, 110 with he sleeve spaces for constrictions 21b, 21c. The hyraulic connections between the respective control slots of he valve and the above-mentioned sleeve spaces are ontinuously open. The control slot 1a is further continuusly connected through hydraulic line 11a, the contriction 21a and a connecting line 23e with the pressure pace 22a in which the spring 13b is located; and control lot In is connected through line 11d, constriction 21d nd line 231 with the pressure space 220 in which the pring 13d is located. The control slot 1b, analogously, l in continuous hydraulic connection through line 11b, onstn'ction 21b and a line 24c with the pressure space :2b of spring 13a; and control slot lb is continuously :onnected through lines 11c, construction 21c and a coniecting line 24] with the pressure space 22:! of spring .30. The illustrated position of the piston sliders correponds to an operating condition in which p,=p

For explaining the operation of the device it may [gain be presumed that the cylinder port just located tbove the neutral axis NA appertains to a cylinder :hamber V condition, that is, the machine piston in his cylinder chamber is just in outer dead-center posiion. Also assume that the stroke volume of the ma- :hine is constant. The control and regulating phenom- :na are in accordance with those explainedflwith refer- :nce to the embodiment of Fig. 3, as will be recognized 'rom the most important operations presently described with reference to the types of operation listed in the tbove-presented table.

(1) Operation type Ia.Control slot 1b is the pressure slot subjected to pressure p,. Control slot 1a is the auction slot subjected to pressure p;. The slider 19c s loaded from spring space 22b by the pressure p and from spring space 22a by the pressure acting upon :he slider in opposition to pressure p;. Consequently, :he piston slider 192 is displaced toward the right until the force of spring 13b balances the hydraulic differ- :nce force. Now the middle portion of the piston slider [9e is efiective, in dependence upon the pressure difference p,p to connect a certain number of auxiliary slots of the series 2b, 3b, 4b. The connected number of auxiliary slots is dependent upon the spring characteristic and the axial spacing between the port openings of lines 6b, 7b, 8b at switching sleeve 20e. As a result, the cylinder ports 5, during CL-rotation, must pass through a certain angle of rotation, namely the compression angle a commencing from the neutral axis NA, until the ports enter in communication with one of the open pressure slots or with the main pressure slot lb itself. At the moment when such hydraulic connection is established, hereinafter briefly called critical moment, the cylinder pressure p, is approximately or accurately equal to p:. The piston slider 19c simultaneously controls the neighboring auxiliary slots of the suction slot 1a and, in the present case, completely opens these auxiliary slots so that they are all in communication with the suction slot la.

The slider 19 is loaded from spring space 22d by the pressure p, and from spring space 22c by the opposed pressure p Consequently, the piston slider 19f moves toward the left until the force of spring 13d balances the hydraulic difference force. This causes the middle portion of piston slider 19f to close a certain number of auxiliary slots of the series 2d, 3d, 4d, this number being dependent upon the magnitude of the pressure ditference p -p the spring characteristic and the axial spacing of the openings of lines 2d, 3d, 4d in switching sleeve 20f. As a result, the cylinder port 5, during CL-rotation, must pass beyond the neutral axis NA through a certain angle of rotation, namely the expansion angle on, until the ports enter into communi- 12 cation with one of the open auxiliary slots or with the main suction slot 1a itself. At the critical moment when such communication becomes established, the cylinder pressure p is approximately or accurately equalto the pressure p The piston slider 19f simultaneously controls the neighboring auxiliary slots of the pressure slot 1b and, in the present case, completely opens these auxiliary slots so that they are all in hydraulic communication with the pressure slot 1b. The machine operates as a pump with a positive value of V and the angles a: and a seen in the direction of rotation,

are fully located behind the neutral axis NA.

(2) Operation type lIIa.Control slot 10 is the pressure slot. Slot 1b is the suction slot. The piston slider 190, following the pressure difference Pz-Ph is displaced toward the left; and slider 19} is displaced toward the right. The auxiliary slots 2b, 3b, 4b of suction slot 1b and the auxiliary slots 2d, 3d, 4d of the pressure slot 1a are completely opened, whereas the auxiliary slots 2a, 3a, 4a of pressure slot 1a and the auxiliary slots 20, 3c, 4c of suction slot 1b are closed in accordance with the particular compression or expansion angle required for V, and V,, respectively. The piston machine operates as a pump with a positive value of V and the angles a: and m seen in the direction of rotation, are entirely located behind the neutral axis NA.

(3) Operation type Ib.In this condition, slot 1b is the pressure slot and 1a is the suction slot. In accordance with the pressure difference p p the piston slider 19c moves toward the right, and the slider 19 moves toward the left. The auxiliary slots 2a, 3a, 4a of suction slot 1a and the auxiliary slots 20, 30, 4c of pressure slot 1b are completely open, whereas the auxiliary slots 2b, 3b, 4b of the pressure slot and the auxiliary slots 2d, 3d, 4d of the suction slot are closed in accordance with the expansion and compression angles required for V, and V respectively. The machine operates as a motor with a positive V value; and the angles my and m seen in the direction of rotation, have their full extent located ahead of the neutral axis NA.

(4) Operation type IIIb.-In this operation, control slot 1a is the pressure slot and 1b the suction slot. Under the pressure difference p,p the piston slider 19e is displaced toward the left and the piston slider 19f toward the right. The auxiliary slots 2b, 3b, 4b of suction slot 1b and the auxiliary slots 2d, 3d, 4d of the pressure slot 1a are completely opened. The auxiliary slots 20, 3a, 4a of the pressure slot 1a and the auxiliary slots 2c, 30, 4c are closed in accordance with the expansion and compression angles required for V, and V, respectively. The machine operates as a motor with a positive V value; and the angles a and ar seen in the direction of rotation, are entirely located ahead of the neutral axis NA.

It will be recognized that in a device for noise reduction according to Fig. 4, all operating conditions characterized by a positive sign of V (displacement volume of machine piston at full stroke) satisfy all requirements. For operation under conditions involving a negative sign of V the hydraulic lines Be and He would. have to be exchanged with the lines 23 and 24]. This can be done when installing the machine, or changeover switching valves may be used for this purpose as will be described in a later place.

FIG. 6

In the embodiment illustrated in Fig. 5, the control slots 1a and lb and the appertaining auxiliary slots correspond, as regards arrangement and functioning, to those described above with reference to Figs. 2 to 4. Similar to the embodiment of Fig. 4, the device is provided with two double-acting piston sliders 25e, 25f which are displaceably guided in respective switching sleeves 26 and 26f. However, whereas in the embodiment of Fig. 4 each double-acting piston controls auxiliary slots of both main control slots, each of the two sliders 25e and 25 in the device of Fig. controls both .groups of auxiliary slots appertaining to only one of the two respective control slots. For this purpose, the lines 20, 342,40 andZd, 3d, 4d of the auxiliary slots adjacent to the left control slot 1a lead to the switching sleeve 26c; and the lines 6b, 7b, 8b and 60, 70, 80 lead to the switching sleeve 26f. The piston slider 25e has a single constriction 27e continuously in hydraulic connection with the control slot 1a through a line 28e. Similarly, the corresponding constriction 27 f of piston slider 25f is continuously in hydraulic connection with control slot 1b through a line 28]. In the illustrated center position, the constriction 27e extends along all openings, located axially beside one another, of the connecting oil lines of groups 6a, 7a, 8a and 6d, 7d, 8d as well as the opening of the line 28c. Analogously, the constriction 27f embraces all openings, located axially beside one another, of the connecting lines 6b, 7b, 8b and 60, 7c, 80 as well as the opening of line 28 The piston slider 25e is subjected to spring force in both directions of displacement due to the action of springs 13a and 13d. Analogously, the piston slider 25f is under the force of opposingly acting springs 13b and 130. The spring spaces, namely the pressure spaces 22a and 22c, are in continuous hydraulic connection with the control slot 1a through a line 29a, the constriction 27e and the line 28:2. The pressure spaces for springs 22b and 22d are hydraulically connected through a line 29 with the sleeve space of constriction 27f, and thence through a line 28f with the control slot 1b. The coaction of the pressures P2 and p with the springs 13a, 13b, 13c, 13d corresponds exactly to that described above with reference to Figs. 3 and 4. The operation of the machine during the various types of operation listed in the foregoing table is as follows:

(1) Operation type Ira-In this condition, slot 1b is the pressure slot and 1a the suction slot. Under the pressure difierence p p the piston slider 25e moves up, and the piston slider 25f moves down. The auxiliary slots 2a, 3a, 4a of the suction slot 1a and the auxiliary slots 2c, 30, 4c of the pressure slot 1b are completely released, whereas the auxiliary slots 2b, 3b, 4b of the pressure slot, as well as the auxiliary slots 2d, 3d, 4d of the suction slot, are disconnected in accordance with the compression and expansion angles required for V and V respectively. The machine operates as a pump with positive V and the angles oa and ar seen in the direction of rotation, are entirely located behind the neutral axis NA.

(2) Operation type IIIa.-In this condition the control slot 111 is the pressure slot, and 1b is the suction slot. Under the pressure difference p -p the piston slider 25e moves down, and piston slider 25 moves up. The auxiliary slots 2b, 3b, 4b of suction slot 1b and auxiliary slots 2d, 3d, 4d of pressure slot 1a are completely opened. Auxiliary slots 2a, 3a, 4a of pressure slot 1a and auxiliary slots 2c, 3c, 40 of suction slot 1b are closed in accordance with the compression and expansion angle required for V and V respectively. The machine operates as a pump with positive V value; and the angles a and w seen in the direction of rotation, have their full extent located behind the neutral axis NA.

(3) Operation type Ib.-Control slot 1b is the pressure slot, and 1a is the suction slot. Under the pressure difierence p,-p the piston slider 25e moves up, and slider 25f moves down. The auxiliary slots 2a, 3a, 4a of suction slot 1a and auxiliary slots 20, 30, 4c of pressure slot 1b are completely released, whereas the auxiliary slots 2b, 3b, 4b of the pressure slot and the auxiliary slots 2d, 3d, 4d of the suction slot are disconnected in accordance with the expansion or compression angle required for V or V The machine operates as a motor with a positive V value; and the angles a: and a seen in the direction of rotation, have their full extent located ahead of the neutral axis NA.

(4) Operation type IIIb.-In this condition, control slot 1a is the pressure slot, and lb is the suction slot. Under the pressure difierence p p the piston slider 25e moves down, and slider 25] moves up. The auxiliary slots 2d, 3d, 4d of the pressure slot 1a are completely released, whereas the auxiliary slots 2a, 3a, 4a of the pressure slot 1a and the auxiliary slots 2c, 3c, 40 of the suction slotare closed in accordance with the expansion and compression angles required for V and V, respectively. The machine operates as a motor with positive V value; and the angles a and a are located ahead of the neutral axis NA seen in the direction of rotation.

In this embodiment of Fig. 5 the springs 13a, 13b must be adapted, as is, the case in the embodiments of Figs. 3 and 4, to the condition (V V max, V required for V adapted in accordance with the condition (V /V max, 21) pp y to a- As shown in the foregoing, a noise reducing device according to Fig. 5 has the elfect that the piston engine satisfactorily runs with optimum noise reduction during all operating conditions involving a positive sign of V 1f the same machine is to be operated under conditions involving a negative sign of V it would be necessary to connect the line 29a with the control slot 1b and the line 29f with the control 'slot in. This can be done when installing the machine or by means of a change-over switching valve as described further below.

FIG. 6

In the modified embodiment illustrated in Fig. 4, the two control slots 1a and 1b with the groups of auxiliary slots 2a, 3a, 411, 2d, 3d, 4d, and 2b, 3b, 4b, 2c, 30, 4c co operate with a switching-valve sleeve 20e provided with a double-acting piston slider 19c, valve springs 13a and 13b, and hydraulic lines 23e and 24a. The design and functioning of these components is similar to the components denoted in Fig. 4 by "the same respective. reference characters. However, in contrast to the embodiment of Fig. 4, the one shown in Fig. 6 lacks the second switching sleeve 20 with lines 23 24f and connecting lines 20, 3c, 40, 110, 2d, 3d, 4d and 11d. In lieu thereof, the device is provided with connecting ducts or lines Zac, 3ac, 4ac which connect the auxiliary slots 2a, 3a, 4a with respective slots 26, '30, 4c. Similar ducts or lines Zbd, 3bd, 4bd connect the auxiliary slots 2b, 3b, 4b with the respective slots 2d, 3d and 4d. The interconnections are continuously open hydraulically.

A prerequisite for the proper functioning of this device is an odd number of machine cylinders and hence a cor respondingly odd number of cylinder ports 5, whereby the formation of undesired short circuit connections be tween two variable-volume cylinder chambers through the last-mentioned connecting ducts or lines is prevented.

The performance of a device according to Fig. 6 is exactly in accordance with the one described with reference to Fig. 4 and for that reason need not be further discussed. Such a noise reducing device is relatively simple and cheap, although it has the disadvantage, compared with devices according to Figs. 3 to 5, that during the automatic regulation of oa and ar only the median values of both controlling magnitudes V and V are taken into account. However, the illustrated device is favorably applicable in such cases where, by virtue of a suitable design of the multi-piston machine-for instance by giving the auxiliary slots 20, 3c, 40 and 2d, 3d, 4d a slight tangential width or small angular extentcare has been taken that, with constant-stroke operation of the,

machine, each angle a or a regulated at the auxiliary slots 2a, 3a, 4a or 2b, 3b, 4b in dependence upon the pressure difference p p by the piston slider 19c and the switching sleeve 20e, has a value of satisfactory approximation.

FIG. 7

The noise reducing devices so far described comprise a particularly designed control apparatus for distributing Analogously, the springs 13c and 13d must becontrol system which automatically affords optimum noise reduction for all types of operation listed in the foregoing table. The main control valve MCV for the liquid pressure medium and also the slot-controlling switching valves SCS comprising two double-acting piston sliders correspond to the embodiment illustrated in Fig. 4. For that reason, the individual components are given the same reference characters as in Fig. 4 to the citent necessary for explaining and understanding the system. A difference of the just-mentioned components in the system of Fig. 7, as compared with the noise reducing device shown in Fig. 4, relates to the springs 13a, 13b, 13c, 13d acting uponthe piston sliders. While in the embodiment of Fig. 4 the two springs correlated to one end of the control slots are adapted to a constant value of V and the other two springs are adapted to a'constant value of V all four springs for the piston sliders 19 and 191 in Fig. 7 are uniformly rated. The rating of the springs is such that, in conjunction with the piston sliders and the axial spacing of the port opemngs for hydraulic lines 6a, 7a, 8a, 6b, 7b, 8b, 60, 7c, 8c and 6d, 7d, 8d, a regulation of the angles a and a, is brought about for the condition V, V,,.=V,.

In order to obtain automatic regulation of the angles a; and a two separate pressure regulators PRL and PRR are provided for the V -side and the V -side of the valve control face respectively. The two pressure regulators are supplied with the pressure dilference p -p =p, and they convert this pressure difference into a pressure p, or p, in dependence upon the variables:

V,,=f( V V V max.) and The converted pressures p. and p are supplied to the slotcontrol switching devices SCS at the V side and V side respectively, so that the value of the angle a or a, is produced in the respective switching devices SCS as a function of all variables involved.

The pressure regulators PRL, PRR are designed as proportional regulators. That is, they always vary the pressure p, irrespective of its absolute magnitude, in a given ratio which, however, may be set to a proper value from the operation controls of the hydraulic machine. Each of the two regulators comprises two control cylinders or bores 30, 31 in which respective controls 32 and 33 are slidable. The two pistons in each regulator abut against the respective arms of a teeter lever 34 to produce mutually opposed torques. Each teeter 34 is mounted on a swing arm 35 linked to the regulator housing 36. The control bores 30 and 31 are closed at the top. The pressure p=p p to be converted is continuously supplied to the control bores 30 through a line 37a or 37b and pushes the control pistons 32 against the respective teeters 34.

In the illustrated normal operating condition, the upper end of each control piston 32 uncovers a lateral port opening of control bore 30, whereby the pressure p is also applied through a line 38 to the interior of the control bore 31 where it imposes a corresponding load upon the control piston 33. When the torque imposed upon the teeter 34 by piston 33 is greater than that produced by piston 32, the piston 33 moves down and the teeter forces the piston 32 up. Then the control piston 32 covers the port of line 38 and thus terminates the equalizing performance. The pressures in the respective control bores 30 and 31 are then related to each other in inverse proportion to the products formed by the cross-sectional area of the control pistons times the instantaneous leverage arm effective at the teeter 34. Consequently the line 39 connected to the end of the control bore is at any time subjected to a pressure whose relation to the pressure p acting in the control bore corresponds to a ratio inverse to that of the instantaneously active leverage arms of the teeter 34.

The control bore 31, too, is provided with a lateral port from which a line 40 leads to a space of negligible or zero pressure, for instance into the housing 36 of the regulater which is under ambient atmospheric pressure. The port of. line 40 is uncovered by control piston 33 during its downward motion at a moment when this piston has already shut off the supply to line 38. Thus the line 40 permits the occurrence of a pressure drop in control bore 31 and line 39.

During operation the following regulating play takes place: Pressure p from line 37a or 37b forces the control piston 32 in Fig. 7 downward. Control piston 32 then uncovers the port of line 38 so that the pressure in control bore 31 increases. This pressure forces the regulator piston 33 downward under the condition that the torque thereby imposed upon teeter 34, in accordance with the piston area and a suitable leverage ratio, can never be smaller than the torque produced by the control piston 32. The teeter 34, now moving counterclockwise, forces the piston 32 upward so that this piston covers the port of line 38 and thus discontinues the supply of pressure to the control bore 31. The torques produced by both pistons are then in equilibrium.

When the pressure p in line 37a or 37b increases, the regulating play repeats itself until a new balance condition is reached. When the pressure p in line 37a or 37b drops, the pressure in line 39 above regulator piston 33 preponderates, and piston 33 moves downward until it uncovers the port of line 40 thus permitting the pressure medium to escape. As soon as the pressure in control bore 31 and line 39 again corresponds to the instantaneous balance condition at the teeter 34, the regulator piston 33 again rises and terminates the escape of medium through line 40. If the two pistons 32, 33 in each regulator have the same diameter, the regulated pressure ratio always corresponds to the effective leverage ratio of the teeter 34.

It is possible to combine the individual variables into a single variable related to the ratio V /V max, and to use this totalized variable for controlling the pressure ratio p/p, or p/p, to be regulated by the pressure'regu- \lators PRL and PRR. The pressure p, or p, is supplied to the slot-control switching devices SCS for the proper V -side or V -side of the rotary control valve MCV, where this pressure imposes a load upon one end of the piston slider, while the other end of the same slider is in communication with a space of negligible pressure through control means still to be described. In the system of Fig. 7 the required dependence of the totalized variable upon the ratio V /V max is secured by controlling the pivot positions of the respective teeters 34, and thus the effective teeter leverage ratio in the two pressure regulators PRL and PRR, in dependence upon the selected setting of the piston-stroke adjusting device of the multi-cylinder engine. For this purpose the strokesetting control means of the machine, such as the control arm Q in Fig. l, are connected by a linking rod (41' in Fig. 1) or other suitable transmission with a lever 41 pivotally mounted in the housing 36 of the pressure regulators. The connection is such that the lever 41 occupies the illustrated mid-position when the piston stroke 17 of the machine is set to zero, and that the lever 41 is turned in one or the other direction to the dot-and-dash positions when the stroke length is increased from zero toward an increasing value of V /V max, the direction.

of lever displacement being dependent upon the delivering direction, i.e. the sign of V A cam member 42 with two symmetrical cam faces is rigidly connected with lever 41 within the regulator housing 36. Cam member 42 is engaged by two cam rollers 45a and 45b journalled on respective swing arms 43 which are pivotally linked to the housing 36. Each of swing arms 43 is linked with one of the swing arms 35 by a linking rod 44 so as to form a linkage parallelogram. When the control lever 41 together with cam member 42 are moved about their common pivot, the linkage parallelogram in each regulator varies the leverage ratio at teeter 34 depending upon the cam contour of member 42. When the cam rollers 45a, 45b occupy the respective innermost positions shown in Fig. 7, the torques produced by the two regulator pistons 32 and 33 under the same pressure in the two control bores 30, 31 are equal or, preferably, the torque of piston 33 is slightly preponderant. This means, that with lever 41 in the illustrated mid-position, the pressure p,,=p regulated by the pressure regulators in the lines 39 is nearly or exactly equal to the difference pressure p=p p supplied through the line 37a or 37b. When the lever 41 is turned away from its normal position, the cam member 42, by virtue of its particular cam contours, is effective to always produce a change in the leverage ratio of the teeters dependent upon the above-mentioned totalized variable, thus also securing a corresponding change in the pressure being regulated.

The above-mentioned totalized variable for the V side (neutral zone of the valve control face corresponding to the smaller cylinder volume) of the rotary side valve differs in value from the :totalized variable applying to the V -side (the other neutral zone corresponding to the larger cylinder volume). In accordance therewith, the cam member 42 possesses for each roller 45a, 45b two different cam portions of different curvature merging at the zero position. For example, when the control lever 41 is turned into the +V -range, shown at the left of lever 41 in Fig. 7, the left-hand pressure regulator PRL regulates the pressure p,, required on the V -side for automatic regulation of the angle a or a whereas the right-hand pressure regulator PRR regulates the pressure p, required for the automatic regulation of the angle a or a, on the V -side of the valve control face. When the control lever 41 is turned from zero position into the V -range, which corresponds to a different deliver-ing direction of the machine operating as a pump, the pressure regulator PRL regulates the pressure p, and regulator PRR the pressure p When the piston machine is operating under a pressure p, of appreciable magnitude, this pressure may have an influence upon the true magnitude of p; and such infiuence, for the reasons already mentioned, must be taken into account if exact performanceof the noise reducing system is to be secured. For this purpose, the lines 460 and 46b extending from respective control slots 1a and 1b are led to a differential pressure regulator DPR which comprises a middle cylinder 47 coaxially joined on both sides with side cylinders 48a, 48b of smaller diameter. The difierential regulator is provided with a stepped piston whose diametrically larger middle portion 49 is slidable and oil-sealed in the middle cylinder 47, and whose two lateral piston members 50 are similarly slidable in the side cylinders 48a and 48b respectively.

The stepped piston is axially movable to a limited extent sufiicient for controlling the ports of two outlet lines 52a and 52b, these ports being located in the middle cylinder 47 close to the respective front sides of the middle piston 49 when the piston is in the illustrated midposition. The outlet lines 52a and 52b are connected through a common line 52 with a space of lower pressure, for instance and as shown, with the interior of the regulator housing 36. Each displacement of the differential piston from the neutral mid-position causes closing of one of the twoou-tlet lines 52a, 52b respectively. Hydraulic connecting lines 53a and 53b open into the respective side cylinders 48a, 48b and are also in communication with the respective axial ends of the middle cylinder 47 so that each of lines 53a or 53b continuously connects one of the respective side cylinders with the one middle-cylinder space remote from that particular side cylinder. The port openings of lines 53a and 53b in the two side cylinders are so located as to become uncovered by the respective side pistons as soon as the middle piston 49, when moving axially, covers the port opening of the one outlet line 52a or 52b connected with the line 53a or 53b just closed.

The performance of the differential pressure regulator is in accordance with the following equation (Eq.):

'P2ib'Px= 'P1+ b'Py or (rgpl)=p px wherein p and p =pressure of control slots 11:, 1b in atmospheres of absolute pressure (ata.);

p =pressure of the outlet line 52 in ata.;

p =derived differential pressure, proportional to the pres sure difference p -p in ata.;

F,,=cross-section area of the lateral piston portions 50;

F =cross-sectional area of the piston middle portion 49 minus the area Fa.

The operation of the differential pressure regulator is as follows:

For explanation the pressure p may be assumed to be 1 ata. (i.e. the equal to ambient atmospheric pressure). One side piston 50 is always loaded by the pressure p the other side piston by the pressure 1,. Hence the stepped differential piston is subject to axial displacement under a force equal to the product Fa (p -p For instance, if p; is effective in side cylinder 48a, then the differential piston of device DPR moves toward the right and first closes the outlet line 52b. This already causes a pressure increase in the annular cylinder space at the right of the middle piston 49 because the oil content in the annular space, previously under little or no pressure because of the outlet line 52b, is now subjected to pressure by the annular portion of piston 49. The displacement of the differential piston toward the right continues as long as the product of the pressure p, in the annular space at the right of the middle cylinder times the area Fb remains smaller than the product Fa (p -p Ultimately the left side piston 50 uncovers the port opening of line 52a. Now the working medium, under the pressure p,, passes from the side cylinder 48a into the line 53a until the pressure in line 53a, and thereby also in the communicating annular space of the middle cylinder 47, has risen to the static equilibrium of the differential piston. As soon as pressure 11,. in line 53a continues to increase (because p, is always greater than p the forces which load the differential piston toward the left become preponderant and the differential piston is again shifted toward the left so that the side piston 50 again covers the port opening of line 53a. Now the pressure p in line 53a has the magnitude corresponding to the foregoing equation (Eq.), whereas the line 53b is without pressure because it now communicates with the escape line 52. As a result, the differential pressure regulator DPR has set itself in accordance with the instantaneously existing values of p, and 17 thus producing the desired differential pressure p,,.

If now, during the further operation of the multi-piston engine, the pressure p, increases or the pressure p decreases, or if both events occur simultaneously, then the above-described regulating performance repeats itself until a new balance condition is obtained. However, if the pressure p, decreases, or if p decreases, or if both events occur, then the forces loading the differential piston toward the left become preponderant; and the piston, now shifting toward the left, uncovers the outlet line 52b until the pressure p in line 53a has declined in accordance with the new datum value.

It will be remembered that the above-described performance of a system according to Fig. 7 relates to operating conditions of the multi-cylinder machine under which the valve control slot in has the pressure p, and slot lb has the pressure p It will be readily understood from the foregoing that when these conditions are reversed, that is, when slot 1a has the pressure p and slot 1b the pressure 17,, so that the differential pressure regulator DPR is loaded through lines 46a and 46b in the inverse relation, the regulating phenomena remain ex- 20 oil-scaled and slidable in the cylinder sleeve. The pressure of respective lines 53a, 53b is passed upon the two axial ends of the switching piston 55 so that the obtainactly as described above, with the only exception that then the difierential pressure p is being built up in the line 53b, whereas line 530 has zero pressure.

In harmony with the automatic regulation of the angles I: and or fully described above with reference to Figs. 3 to 5, it has been assumed in the foregoing description of Fig. 7 that the switching-valve devices SCS, hydraulically connected with the rotary-slide control valve MCV of the machine, will operate under the full differential pressure p -p and without any coaction of the pressure ratio regulators PRL, PRR if the machine is operating under the condition +V V /V max.=l, or V;;, V /V max. In other words, the two ratio regulators are supposed to permit through-passage of the full pressure difference p,-p when V =zero, i.e. when the ratio regulators have the neutral setting shown in Fig. 7.

In order to satisfy this requirement, thedifierential pressure regulator DPR as shown in Fig. 7 must meet the condition that the pressure p is zero or negligible, and that the area Fb is equal to the area Fa. With these pressure and area ratings, the differential pressure regulator DPR actually regulates the pressure p to be equal to the pressure difference p,p and the above-presented equation (Eq.) converts into the specific case: Pr Pa'-P1- It is often not desirable to operate the pressure regulating devices and the switching valve devices with the full operating pressure of the hydraulic machine. It is apparent from the equation (Eq.) that by suitably dimensioning the diameter ratio and hence the area ratio of the side pistons 50 and the middle piston 49, it is readily possible, when making p,=zero, to operate the same regulator as a difierential ratio regulator whose lines 53a and 53b carry the respective pressures p,=Fa/Fb (p -p and p,=zero, or vice versa. However, it is also readily possible to adapt the spring components of the slot-control switching devices SCS in accordance with a pressure, taken from the difierential ratio regulator, which is propor. tional to the pressure difference Pg-P1 but smaller than this difierence. Any such modification of the differential pressure regulator does not necessitate a change in the design of the two pressure-ratio regulators PRL and PRR that are controlled by the stroke-length adjusting device of the hydraulic machine.

As described, the pressure p is supplied to the two ratio pressure regulators PRL, PRR from line 53a or line 53b through lines 37a and 37b, depending upon the operating condition of the hydraulic machine. It follows that it is necessary to prevent the two lines 53a, 53b from being in short-circuit connection with each other which would disturb the functioning of the differential pressure regulator. For this purpose, the two lines 53a and 53b according to Fig. 7 are connected with a hydraulically actuated change-over switch RS operating essentially like a three-way slide valve or a two-way valve. The change-over switch RS comprises a cylinder sleeve 54 closed at both ends, and a switching piston 55 ing pressure p, always shifts that piston against a limiting stop in opposition to the force acting upon the other end of the switching piston and corresponding to the effective pressure (practically equal to zero) in the outlet line 52. During such displacement, the switching piston 55 uncovers a lateral port 56a or 56b of the cylinder sleeve 54, so that the pressure p,, acting through the ports and through respective lines 37a, 37b and interconnecting line 57, is imposed upon both pressure ratio regulators PRL, PRR.

During each switching operation of the change-over switch RS, the switching piston 55 first covers one of the port openings 56a, 56b before it opens the other for the passage of the pressure 11,; and this prevents in all cases- If desired, the lines 39 coming from the pressure regulators PRL, PRR and carrying the pressures p and p could simply be connected to the respective sides of the cylinder sleeves of the slot-control switching devices SCS. A hydraulic multi-piston machine thus equipped would satisfactorily operate under all those operating conditions during which the (plus or minus) sign of V does not change. In practice, however, such change takes place with each hydraulic machine of this type when its piston-stroke varying control is displaced through the zero-stroke position into the range of the opposite direction of delivery; and this occurs even if, due to extraneous effects, the pressure difierence Pg-P1 at the control slots 1a, 1b of the valve control face changes its direction. Therefore, in order to have the noise reducing device according to Fig. 7 operate satisfactorily under all feasible operating conditions, the lines 39 carrying the pressures p, and p, are connected to two hydraulic reversing switches CS whose performance is essentially equivalent to two five-way valves or to four three-way valves, or to a single eight-way valve,- and which accord- 'ingly may also be formed of the just-mentioned types of devices. In the embodiment of Fig. 7, the two hydraulic reversing switches CS comprise each a cylinder bore 58 of the regulator housing 36 and a control piston 59a or 59b oil-sealed and displaceable in the bore. In the illustrated example, the two control pistons are axially loaded by respective springs so that the piston bottoms are forced against the top of the cam member 42. Consequently, whenever the control lever 41 and cam member 42 are turned away from the neutral mid-position, the two switch pistons 59a, 5% are likewise displaced from their neutral mid-position upwardly or downwardly as the case may be. In this manner, the two hydraulic switches CS are so coupled with the stroke-length controls of the hydraulic machine that the switches operate in dependence upon the sign of V The control pistons 59a, 59b are each provided with two constricted portions 60 of the kind customary with. five-way control valves. Each two lines 61a, 62a or 61b, 62b communicate with the respective control bores 58 and are in continuous connection with one of the constrictions 60 of the correlated control piston 59.- These lines 610, 62a and 61b, 62b serve for applying the respective pressures p, and p; to the switching devices.

The lines 39 coming from the pressure regulators PRL, PRR open each into one of the respective control bores 58 at such a location that the lines 39 are closed by the piston portion between the two constrictions 60 when the control pistons 58 are in mid-position as illus- 1 trated. When each control piston 58 is being displaced gible pressure (such as atmospheric pressure), which space in the illustrated example is formed by the interior of the regulator housing 36. The outlet line 63 communicates with each of the two control bores 58 at two places so located that the outlet line 63 is just kept open by the control piston 59a or 59b when this piston is in mid-position but is closed when the piston performs a given amount of displacement, such closing being effected in dependence upon the direction of displacement by one or the other end portions of the correlated control piston 59a or 59b.

The two cam-controlled change-over switches CS operate as follows: In the illustrated neutral mid-position of control lever 41 and cam member 42, the lines 39 are completely closed. Each displacement of control lever 41 from the neutral position causes lifting of one and lowering of the other control pistons 59a, 59b. This causes the constrictions 60 of the pistons to connect the zero-pressure line 63 with one of the lines 61a, 62a and one of lines 61b, 6217, whereas the other one of these two pairs of lines is simultaneously connected with the line 39. Consequently, the left-hand pressure regulator PRL,

when control lever 41 is turned into the positive range,

supplies the line 610 with a pressure equal to p,,, and the right-hand pressure regulator PRR supplies to the line 62b a pressure equal to 12 while the lines 62a, 62b are connected with the zero-pressure outlet line 63. On the other hand, when the control lever 41 is turned into the negative range, the left-hand pressure regulator PRL supplies the line 62a with a pressure equal to p,, and the right-hand pressure regulator PRR supplies line 61b with a pressure equal to p while the lines 61a and 62.5 are connected with the outlet line 63. When operating the hydraulic machine as a pump in CL rotation, the positive V -range in the example of Fig. 7 corresponds to a V value in the range of the upper half of the valve control face; and the negative range of V corresponds to V in the range of the lower half of the valve control face; and in each case the value V is located on the opposite side.

The two hydraulic change-over switches CS actuated from the piston-stroke control of the hydraulic engine may also be combined into a single switching device whose control piston is then given a correspondingly greater length and is provided with all constrictions and ports for the switching of the hydraulic lines connected thereto.

Series connected, hydraulically, with the last-mentioned switches are two reversing-switch devices hydraulically actuated by the pressure 12,, and having an over-all performance equivalent to that of two five-way valves or four three-way valves, or an eight-way valve. These two reversing-switch devices are combined with the above-described change-over switch RS so as to form a single multiple switch unit. This combination of switching means is obtained by giving the above-described switching piston 55 four constrictions 64a, 64b, 64c, 64d and providing the appertaining control sleeve 54 with the proper control ports. Accordingly, the constrictions 64a, 64b operate to switch lines 61a, 62a relative to their connection with the lines 66a, 66!; leading to the cylinder sleeve 29e in device SCS; and the constrictions 64c, 64d control the connection of the lines 61b, 62b with the lines 66c, 66d leading to the cylinder sleeve 20f. Thus, each distribution of the pressures p p, onto the two control slots 1a, 1b is correlated to a given switch position of device RS and hence to a given connection of the hydraulic lines, which distribution always adjusts itself automatically because the hydraulic control of the multiple switching valve RS is dependent upon the two possible directions of the pressure difference p p between the two control slots 1a and 1b.

The cooperation of all above-described components of the system according to Fig. 7 will be described presently in abbreviated form with reference to all possible operat 22 ing conditions as listed in the table presented in the introduction of this specification.

Operation type Ia: Control slot 1a under pressure 12 Control slot 1b under pressure 12 Volume V occurs in the upper portion and volume V in the lower portion of the valve control face. Control lever 41 is in the +V -range. The difl'erential pressure p, obtains in line 53b, pushes the control piston 55 toward the left, passes from control sleeve 54 through port 56b, acts upon the two control pistons 32, and is converted by regulator PRL into the pressure p under control by the shallower cam portion of cam member 42. Pressure p, acts through line 39, switch CS, line 61a, switch RS and line 66b upon the left end of piston slider 19:: in SCS, while the right end of slider 19e is not pressure-loaded because it is connected with the interior ofregulator housing 36 or a reservoir for the hydraulic working medium, through line 66a, switch.RS, line 62a and the upper constriction 60 of the left-hand change-over switch CS. Piston slider 19e in the sleeve 20:: moves toward the right until balance is established with the force of spring 13b. Thus, the piston slider 19e, depending upon the particular magnitude of p disconnects a definite number of the auxiliary slots 2b, 3b, 4b, in the sequence here given, from the correlated main slot 1b. As a result, a positive compression angle a adjusts itself which results in the pressure balance required for reducing noise at the moment when a communication is established between the individual cylinder chambers of the machine with the control slot 1b. (For brevity, the moment just defined will be referred to as the critical moment.)

The pressure regulator PRR modifies the pressure p under the effect of the steeper cam portion of cam member 42 into the pressure 12,. Pressure p acts through line 39, switch CS, line 62b, switch RS and line 66d upon the right end of piston slider 19f, while the left end of slider 19 is not under pressure because it is connected with the interior of the regulator housing 36 through line 66c, switch RS, line 61b and the lower constriction 60 of the right-hand change-over switch CS. As a result, the piston slider 19 moves toward the left until equilibrium is established with the force of spring 1311. Slider 19f thus disconnects from the control slot 1a a given number of auxiliary slots 2d, 3d, 4d in the sequence here given, the number depending upon the magnitude of p;. In this manner, a positive expansion angle ac adjusts itself which results in the pressure balance required for noise reduction at the critical moment of commencing communication between the slot 10 and the cylinder chamber of the machine.

Operation type Ib.-Compared with type Ia, the hydraulic machine merely changes its direction of rotation from CL to ACL and runs, not as a pump, but as a motor. The above-considered compression angle +11, in the right upper portion of the valve control face now becomes the expansion angle +a the above-considered expansion angle +a in the left lower portion of the valve control face becomes the compression angle +11 and all operations of the system remain otherwise as described above.

With all possible conditions of operation according to the above-presented table, the angles oa and on on the V -side of the valve control face are equal to each other; and there is also equality of the angles a and ar on the V -side of the control face.

Operation type Ila.Pressure p in control slot 1b, pressure 11 in slot 1a. Volume V occurs in the lower portion, and volume V in the upper portion of the valve control face. Lever 41 is in the -V -range. The difference pressure p occurs in line 53a, moves the switching piston 55 of reversing switch RS to the right, acts in sleeve 54 through port 560 and onto the tWO respective pistons 32 of pressure regulators PRL and PRR. Regulator PRL converts pressure p into the pressure p; under control by the steeper cam curve of member 42. Pressure p acts through line 39, switch CS, line '23 62a, switch RS and line 66b onto the left end of piston slider 19e in slot control switch SCS, while the right end of slider 19c is simultaneously connected with zero pressure, namely with the interior of regulator housing 36, through the line 66a, switch RS, line 61a and the lower constriction 60 of switch CS (left). As a result, piston slider 19 moves in sleeve 20c of SCS toward the right up to the point where balance occurs with the force of spring 13b. Thus the slider 19c separates a certain number of the auxiliary slots 2b, 3b, 4b, in this sequence, from the main slot 1b, this number depending upon the magnitude of 17;. In manner, a positive compression angle q is adjusted which results in the equalization of pressure required for noise reduction at the critical moment of commencing communication between an individual cylinder of the machine with the control slot 1b.

The pressure regulator PRR modifies the pressure p into the pressure p. under control by a shallower cam curve of member 42. Pressure p, acts through line 39, switch CS, line 61b, switch RS and line 66d onto the right end of piston slider 19 in slot control switch SCS, while simultaneously the left end of slider 19) is connected with zero pressure through line 660, RS, line 62b and the upper constriction 60 of switch CS (right). Consequently, the piston slider 19 moves toward the left, up to the point of balance with the force of spring 13d and thus hydraulically disconnects a number of auxiliary slots 2d, 3d, 4d, in this sequence, from the main slot 1a, this number depending upon the magnitude of p Thereby a positive compression angle a is adjusted which results in the pressure equalization required for noise reduction at the critical moment relative to slot 1a.

Operation type Ilb.In this case, the hydraulic machine, compared with operation type Ila, merely changes its direction of rotation from CL to ACL and runs as a motor. The compression angle +n in the left lower quadrant of the valve control face now becomes the expansion angle +a the previously considered expansion V, angle +a, in the right upper quadrant becomes the compression angle +a and all switching operations of the system remain otherwise unchanged.

Operation type lIIa.--Pressure p in control slot 1b, p, in slot la. Volume V in upper portion, volume V in lower portion of valve control face. Lever 41 in range +V The difference pressure p occurs in line 53a, shifts the switching piston 55 in RS toward the right, passes through sleeve 54 and port 56a, and acts upon the two pistons 32 of PRL and PRR. Regulator PRL converts p, into pressure p. under control by the shallower cam curve of member 42. Pressure p acts through line 39, CS, line 61a, RS and line 66a upon the right end of piston slider 19:: in SCS, while the left end of piston 19a is connected to zero pressure through line 66b, RS, line 62a and the upper constriction 60 of switch CS (left). As a result, the slider He moves toward the left in sleeve 20:: of SCS until balance is obtained with the force of spring 13a and, depending upon the magnitude of p... disconnects a number of the auxiliary slots 2a, 3a, 4a, in this sequence, from the main slot 1a. As a result, a negative compression angle a: adjusts itself for equalization of pressure at the critical moment of commencing communication between an individual cylinder chamber and the control slot 1a.-

The pressure regulator PRR modifies the pressure p into the pressure p; under control by the steeper curve of cam member 42. Pressure p acts through line 39, switch CS, line 62b, switch RS and line 660 upon the left end of piston slider 19f in switch SCS, while the right end of the same piston slider is connected with zero pressure through line 66d, RS, line 61b and the lower constriction 60 of CS (right). The piston slider 19f in switch SCS moves toward the right until balance is established with the force of spring 130 and thus separates, in dependence upon the magnitude of p a corresponding number of the auxiliary slots 1c, 3c, 4c, in this sequence, from the main slot 1b, whereby the proper negative expansion angle a, is adjusted as required for pressure equilibrium at the critical moment of commutation.

Operation type IIIb.Compared with type IIIa, the hydraulic machine only changes its direction of rotation from ACL to CL and runs as a motor. The previous compression angle a in the upper left quadrant of the valve control face now becomes the expansion angle a,, the previous expansion angle er in the lower right quadrant becomes the compression angle otherwise all switching operations of the system remain unchanged.

1 Operation type IVa.p obtains in control slot 1a, p, in slot 1b. Volume V, is located below, V above at the valve control face. Lever 41 is in range V;;. The difference pressure p, occurs in line 53b, pushes the piston 55 of switch RS toward the left, acts through sleeve v 54 and port 56b upon the two pistons 32 of PRL and PRR. PRL converts p, into p under control by the steeper cam curve of member 42. Pressure p acts through line 39, CS, line 62a, RS and line 66a upon the right end of piston slider 19:: in SCS, while the left end of the same piston is connected to zero pressure through line 66b, RS, line 61a and the lower constriction 60 of CS (left). The piston slider 19c in sleeve 20c moves toward the left until balance is reached with the force of spring 13a, and thus disconnects, in dependence upon the magnitude of p,, a corresponding number of the partial slots 2a, 3a, 4a, in this sequence, from control slot 1a. As a result, a negative expansion angle on is adjusted as required for pressure equalization at the critical moment.

Regulator PRR modifies pressure p into 12. under control by the shallower cam curve of member 42. Pressure 2,, acts through line 39, RS, line 61b, and line 660 upon the left end of piston slider 19 in SCS, while the right end of slider 19f is connected to zero (atmospheric) pressure through line 66d, RS, 62b, and the upper constriction 60 of switch CS (right) or the control piston 59a of switch CS. Piston slider 19f, under pressure p,, moves to the right up to equilibrium with spring 13:: and thus disconnects, in dependence upon the'magnitude of pressure p, a given number of the auxiliary slots 20, 30, 4c, in this sequence, from the main slot 1b, whereby the proper negative compression angle a is adjusted.

Operation type lVb.Compared with operation type No, the hydraulic machine changes its direction of totation from ACL to CL and runs not as a pump but as a motor. The previous compression angle a in the lower right quadrangle of the valve control face hecomes the expansion angle -a the previous expansion angle in the left upper quadrant becomes the compression angle a otherwise all switching operations of the system remain unchanged.

FIG. 8

The noise reducing apparatus for multi-piston machines illustrated in Fig. 8 comprises a rotary slide valve MCV and a slot control switch SCS corresponding to those illustrated in Figs. 4 and 7 and described in the foregoing. The apparatus of Fig. 8 is likewise suitable for all types of operation listed in the above-presented table. An essential difference, compared with the embodiment of Fig. 7, resides in a particular design of the mechanically controlled pressure regulators PRL and PRR which, in the system of Fig. 8, simultaneously function as the series-connected and likewise mechanically actuated change-over switch (CS in Fig. 7) and thus afford a simplification of the entire system.

The two pressure regulators PRL, PRR are of identical design. Each comprises two cylinder bores 70a and 70b of the regulator housing 71, and two respective control pistons 72a and 72b, oil-sealed and displaceable in the cylinder bores, which have their illustrated lower end abut against the two respective arms of a teeter 73.

The teeter 73 is pivotally mounted on a swing arm 74 

